1. Field of the Invention
The present invention relates to a fiber for clothing. Specifically, the present invention relates to a novel cellulosic fiber or a novel synthetic fiber, whose monofilament is covered with a crosslinked enzyme protein layer on the surface thereof: and to a production method of the fiber.
2. Discussion of the Related Art
Feeling, strength, hygroscopicity, and other physical properties of a natural cellulose such as cotton and hemp, and a regenerated cellulose such as viscose rayon are closely associated with the internal structure of their monofilament made up of cellulose molecules, such as crystallinity (degree and orientation of crystallization) and lamella structure (micro-fibril and fibril). When a cellulosic fiber is chemically treated, not only the surface but also the internal structure of its monofilament are affected, which may in some cases impair advantageous properties of the original cellulosic fiber.
If only the surface of a monofilament can be modified without changing the internal structure thereof, novel functions can be added to the fiber without varying the properties proper to a cellulosic fiber. Such novel functions can add a great value to a cellulosic fiber in developing their applications for clothing.
For selectively improving the monofilament surface of a cellulosic fiber, there have been proposed a number of methods wherein a protein with a molecular weight that is too high to penetrate the monofilament is used to form a protein layer selectively on the single monofilament surface.
For example, a natural cellulose fiber is immersed in a dilute solution of a water-soluble protein to adhere the protein onto the fiber's surface, followed by binding the fiber and the protein by crosslinking, to form a protein Layer on the fiber's surface (Japanese Patent Laid-Open No. 61-245374).
However, these methods are faulty in that the protein adheres unevenly to the single fiber surface, failing to give an even layer over the entire yarn. In fact, when a fiber on which a protein layer has been formed by the above-described method is dyed with an acid dye, uneven dyeing occurs over the entire yarn, indicating that even protein layer is not obtained on each fiber surface of the yarn.
A natural cellulose fiber, and a regenerated cellulose fiber such as viscose rayon show fibrillation on the monofilament surface after repeated wearing and washing, which can result in fuzz and pilling. Such fuzz and pilling can alter cloth feeling and, in some cases, deteriorate the feeling due to hardening. Other undesirable changes caused by fuzz and pilling include luster reduction. To prevent the deterioration of feeling and the reduction of luster in these fibers, it is necessary to prevent fuzz and pilling and suppress fibrillation, a cause of fuzz and pilling.
Conventional techniques for suppressing fibrillation include the method in which a fiber is swollen by immersing a fabric of the fiber in an aqueous solution of a caustic alkali, and the method in which the cloth is treated with a crosslinking reagent for cellulose (e.g., urea-formalin resin, melamine resin, glyoxal resin) (Japanese Patent Laid-Open No. 62-85082).
The above methods are effective in suppressing the fibrillation on the monofilament surface and keeping luster of the fiber. However, the treatment with a crosslinking reagent for cellulose causes a structural change due to cellulose-to-cellulose crosslinking within a single fiber/monofilament. This results in a change in feeling, and, in some cases deterioration of feeling. Therefore, in order to suppress fibrillation without impairing feeling of the fiber, a cellulosic fiber whose monofilament surface is selectively modified without changing internal structure, and a method for such modification have been sought.
On the other hand, synthetic fibers are less comfortable to the wearer in terms of feeling and touch in comparison with natural fibers, such as wool and silk. This is attributable to the fact that a petroleum-based synthetic fiber has low water absorbency and hygroscopicity compared with a natural fiber, because the surface of the fiber is hydrophobic, although they have excellent mechanical strength and other good properties. As solution to these problems, various chemical treatments have been performed to give hydrophilicity to synthetic fibers. For example, a hydrophilic group, such as the hydroxyl group, amino group and carboxyl group, is introduced to the monofilament surface by a chemical reaction, or the monofilament surface is made porous by a plasma treatment. However, the former method is faulty in that overreaction can result in considerably reduced fiber strength, because reaction control during the treatment of the monofilament surface is difficult. The latter method has a problem that it requires large-scale equipment. It is also possible to give hydrophilicity to a synthetic fiber by immobilizing a substance having a hydrophilic group onto the surface of constituent fibers of a synthetic fiber using a crosslinking agent. One such method, for example, uses a polyamino acid and a crosslinking agent to form a layer on the synthetic fiber surface to give hydrophilicity (Japanese Patent Laid-Open NO. 3-199471).
In the above method, however, it is difficult to form a layer of polyamino acid having a constant molecular weight by controlling polyamino acid polymerization. Therefore, the layer is likely to form not only on the monofilament surface but also over the yarn or even over the entire cloth, depending on molecular weight, so that the flexibility of fiber is very restricted even though hydrophilicity can be given to the fiber, resulting in deterioration of feeling due to fiber hardening. It is therefore important that the treatment to give hydrophilicity does not expand beyond the level of a monofilament of a yarn. So, there is a need of an appropriately modified synthetic fiber and a method for such modification.